Uroptychus zigzag, Baba, 2018

Baba, Keiji, 2018, Chirostylidae of the Western and Central Pacific: Uroptychus and a new genus (Crustacea: Decapoda: Anomura), Tropical Deep-Sea Benthos (Mémoires du Muséum national d'Histoire naturelle 212), pp. 1-612 : 566-570

Uroptychus zigzag n. sp.

Figures 285 , 286

TYPE MATERIAL — Holotype: Vanuatu. MUSORSTOM 8 Stn CP 983, 19°21.61’S, 169°27.76’E, 480- 475 m, 23.IX.1994, ♂ 4.3 mm ( MNHN-IU-2014-17093 ) . Paratypes: Vanuatu. Collected with holotype, 1 ♂ 4.0 mm, 1 ov. ♀ 5.1 mm ( MNHN- IU-2014-17094) . New Caledonia, Norfolk Ridge. NORFOLK 2 Stn DW2063, 24°41’S, 168°40’E, 624-724 m, 25.X.2003, 1 ♂ 3.4 mm (MNHN-IU-2014-17095) . Indonesia, Kai Islands. KARUBAR Stn CP16, 5°17’S, 132°50’E, 315-349 m, 24.X.1991, 1 ♀ 4.7 mm (MNHN-IU-2014-17096).

ETYMOLOGY„ The specific name is a noun in apposition from the French zigzag (zigzag), referring to the zigzag arrangement of flexor marginal spines of P2-4 propodi displayed by the new species.

DISTRIBUTION„ Vanuatu, Norfolk Ridge and Kai Islands ( Indonesia); 315- 724 m.

SIZE„ Males, 3.4-4.3 mm; females, 4.7, 5.1 mm; ovigerous female, 5.1 mm.

DESCRIPTION„ Medium-sized species. Carapace: Broader than long (0.7-0.8 × as long as broad); greatest breadth 1.8 × distance between anterolateral spines. Dorsal surface polished, moderately convex from side to side, more distinctly so from anterior to posterior, without depression; small spines mesial to fourth lateral marginal spine, another smaller spine directly behind each anterolateral spine and a few denticles on posterior lateral portion of branchial region; rarely several tiny spines in epigastric row (female, MNHN-IU-2014-17096). Lateral margins convexly divergent posteriorly, somewhat constricted at level of insertion of P1, bearing 12 spines (5 in front of and 7 behind constriction): first spine (anterolateral) strong, directed somewhat anterolaterally, overreaching smaller lateral orbital spine; second and third subequal and smaller than first, both situated ventral to level of other spines; fourth subequal in size to first, occasionally bifurcate dorsoventrally, closer to third than to fifth; remaining spines behind constriction or on posterior branchial margin nearly contiguous at base to one another, posteriorly diminishing, some of these often laciniate or bifurcate, last spine situated near posterior end of margin. Rostrum narrow triangular, with interior angle of 27-35°; length about half or less than half that of remaining carapace, breadth much less than half carapace breadth at posterior carapace margin; dorsal surface somewhat concave; ventral surface horizontal. Lateral orbital spine slightly anterior to level of anterolateral spine, and separated by basal breadth of that spine. Pterygostomian flap anteriorly sharp angular, produced to distinct spine, bearing 1-3 spines near anterior end of linea anomurica (absent in male paratype MNHN-IU-2014-17095) and additional few spines on anterior lower surface; height of posterior portion 0.5 × that of anterior portion.

Sternum: Excavated sternum with longitudinal ridge in midline on surface, anteriorly bluntly produced. Sternal plastron 1.4 × broader than long (three-quarters as long as broad), convexly divergent posteriorly. Sternite 3 weakly depressed, anterior margin gently concave, with small V-shaped median notch lacking flanking spines. Sternite 4 with convex anterolateral margin anteriorly ending in a few tiny spines; posterolateral margin about half length of anterolateral margin. Anterolateral margin of sternite 5 strongly convexly divergent posteriorly, 1.3 × longer than posterolateral margin of sternite 4.

Abdomen: Smooth and glabrous. Somite 1 without transverse ridge. Somite 2 tergite 3.2-3.5 × broader than long; pleuron posterolaterally bluntly angular, lateral margin moderately concavely divergent posteriorly. Pleuron of somite 3 posterolaterally angular. Telson about half as long as broad; posterior plate 1.2-1.4 × longer than anterior plate, posterior margin feebly concave.

Eye: 2.0-2.4 × longer than broad, slightly falling short of rostral tip, distally somewhat narrowed. Cornea about half as long as remaining eyestalk.

Antennule and antenna: Ultimate article of antennular peduncle 2.3-3.0 × longer than high. Antennal peduncle overreaching cornea, barely reaching rostral tip. Article 2 with short lateral spine. Antennal scale 1.4-1.5 × as broad as article 5, distinctly overreaching peduncle, reaching apex of rostrum. Distal 2 articles unarmed; article 5 1.0-1.3 × longer than article 4, breadth 0.5-0.7 × height of ultimate article of antennule. Flagellum consisting of 12-13 segments, far falling short of distal end of P1 merus.

Mxp: Mxp1 with bases very close to each other. Mxp3 with sparse soft setae on ischium, merus and carpus. Basis without denticles on mesial ridge. Ischium having flexor margin roundly ridged distally, crista dentata with small denticles. Merus 1.8 × longer than ischium, with well-developed distolateral spine and 2 small flexor marginal spines (obsolete in ovigerous female paratype) distal to midlength; mesial face somewhat concave; flexor margin sharply ridged. Carpus with distolateral spine and occasionally a few eminences on extensor surface.

P1: 5.7-6.1 × (males), 4.8 × (ovigerous female) longer than carapace; with soft setae, especially numerous along mesial margin. Ischium dorsally with short, basally broad, depressed spine, ventromesially with 5 or 6 short spines, without distinct subterminal spine. Merus 1.2-1.3 × (1.0 × in ovigerous female paratype) longer than carapace; a few to a number of denticle-like processes along proximal half of mesial margin and a few small spines on proximal ventral surface; dorsal terminal margin with 4 tubercle-like small spines, ventral terminal margin with obtuse mesial and lateral spines. Carpus 1.3-1.4 × longer than merus, dorsally with a few tubercles proximally and a few obsolescent terminal tubercles, ventrally with distomesial and distolateral processes, both blunt and short. Palm 3.3-3.8 × longer than broad in both sexes, 1.1-1.3 × longer than carpus; surface smooth. Fingers proportionately broad, not gaping, distally incurved, crossing when closed; opposable margins sinuous, without strong process; movable finger 0.4-0.5 × length of palm.

P2-4: Broad relative to length, moderately depressed mesio-laterally, with soft fine setae more numerous along dorsal and extensor margins. Meri unarmed; length-breadth ratio, 3.2-3.9 on P2, 3.1-3.9 on P3, 2.2-3.1 on P4; P2 merus slightly narrower than, and as long as or slightly shorter than P3 merus, 0.8-1.0 × length of carapace, 1.1-1.2 × longer than P2 propodus; P3 merus subequal to P3 propodus; P4 merus 0.6-0.7 × length of and 0.7-0.9 × breadth of P3 merus, 0.8 × length of P4 propodus. Carpi subequal on P2-3, P4 carpus 0.7-0.8 × length of P3 carpus, about half length of propodus on P2 and P3, slightly less than so on P4. Propodi shorter on P2 than on P3 and P4, P3 propodus usually longest; flexor margin medially convex, ending in pair of spines preceded by 6-7 slender spines on P2, 5 or 6 spines on P3, 4-6 spines on P4, those on P2 and P 3 in zigzag arrangement, placed on distal half, ultimate of these spines more remote from distal pair than from penultimate. Dactyli slightly longer on P3 and P4 than on P2, slightly shorter than carpus (dactyluscarpus length ratio, 0.8 on P2 and P3, 0.9-1.0 on P4), half as long as propodus; flexor margin curving at proximal quarter, ending in slender spine preceded by 10-12 relatively broad, subtriangular, somewhat inclined spines diminishing toward base of article.

Eggs. Number of eggs carried, 17; size, 1.23 mm × 1.37 mm - 1.27 mm × 1.53 mm.

REMARKS„ The new species resembles U. duplex n. sp. and U. macrolepis n. sp. (see above) in having a spinose carapace lateral margin, the antenna unarmed on articles 4 and 5, with the antennal scale reaching article 5, the Mxp3 ischium with rounded distal end of flexor margin, the P2-4 propodi distally broadened, and in the spination of the P2-4 dactyli. Uroptychus zigzag differs from U. macrolepis in having 12 instead of 8 or 9 spines on the carapace lateral margin; the spines on the posterior branchial margin are broad at base (distally laciniate or bifurcate) instead of much smaller (narrowed at base); the eyes are shorter relative to breadth (2.0-2.4 instead of 2.6-3.2 times longer than broad); and the anterolateral spine of the carapace is much larger instead of slightly larger than the lateral orbital spine. Uroptychus duplex is distinguished from U. zigzag by the carapace being much broader than long (breadth 1.7 versus 1.3 times length); the posteriormost of the lateral carapace spines is situated on the posterior quarter rather than near the posterior end; the sternal plastron has the lateral extremities strongly rather than gently divergent posteriorly; the anterior margin of sternite 3 is transverse on the median third instead of concave; and the lateral orbital spine is much smaller compared with that of U. zigzag .

Uroptychus zigzag also resembles U. megistos n. sp. (see above) in having the spinose carapace lateral margin and the inflated flexor margin of the P2-4 propodi, from which it can be readily distinguished by the following: the distal two articles of the antennal peduncle are unarmed instead of bearing a strong distomesial spine; the P2 merus is subequal to or slightly shorter instead of consistently longer than the P3 merus; and the ultimate of the flexor marginal spines of the P2-4 dactyli is much more slender instead of stronger than the penultimate.

Figures

FIGURE 285 Uroptychus zigzag n. sp.,holotype, male 4.3 mm (MNHN-IU-2014-17093).A, carapace and anterior part of abdomen,proximal part of right P1 included, dorsal. B, same, lateral.C, sternal plastron, with excavated sternum and basal parts of Mxp1. D, telson. E, left antenna,ventral.F, left Mxp3,ventral.G, same,lateral.H, same,ventromesial.I, left P1,proximal part,ventral.J, same,proximal articles omitted, dorsal.Scale bars: 1 mm.

FIGURE 286 Uroptychus zigzag n.sp.,holotype,male 4.3 mm (MNHN-IU-2014-17093).A, right P2,lateral.B, same,distal part,setae omitted,lateral.C, same,mesial. D, right P3, setae omitted, lateral. E, same, distal part, setae omitted, lateral. F, right P4, setae omitted, lateral. G, same, distal part, setae omitted, mesial.Scale bars: 1 mm.